In order to evaluate the reliability, e.g. of a hydraulic accumulator, it is known to mount such an accumulator fitted with a flexible separator on a test bench that includes means for causing the volume of liquid to vary cyclically, thereby deforming the flexible separator. That method of testing the reliability of a separator requires the test bench to be fitted with a hydraulic circuit that is complex and relatively vulnerable, in particular because of the need to provide means such as, for example: a four-port valve for reversing the flow direction of liquid through the accumulator, so as to vary the volume and the deformation of the separator. Furthermore, the inertia and the head losses inherent to such a hydraulic circuit limit the rate at which deformation cycles can alternate. The duration of reliability tests for a large number of cycles is therefore very long. That is why, for industrial and economic reasons, one is often encouraged to limit the number of cycles. That raises problems in certain applications where reliability needs to be very high and where it is desirable to continue testing beyond 10,000,000 cycles, i.e. all the way to rupture even though testing is often presently limited to no more than 2,000,000 cycles, for the reasons mentioned above.